Every Pixar movie is connected. Here is the list of them: A Bug’s Life Toy Story 2 Monsters Inc. Finding Nemo The Incredibles Cars Ratatouille Wall-E Up Toy Story 3 Cars 2 Brave Monsters University Let's read the details.
That could explain Sully’s reaction when he opened Boo’s door again. Maybe when the door was fractured, it altered the destination and opened the door into her workshop rather than her childhood bedroom.